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E.P.D.M :-
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EPDM rubber (ethylene propylene diene Monomer (M-class) rubber),[1][2] a type of synthetic rubber, is an elastomer which is characterized by wide range of applications.The E refers to Ethylene, P to Propylene, D to diene and M refers to its classification in ASTM standard D-1418. The “M” class includes rubbers having a saturated chain of the polymethylene type. The diene(s) currently used in the manufacture of EPDM rubbers are DCPD (dicyclopentadiene), ENB (ethylidene norbornene) and VNB (vinyl norbornene).
The ethylene content is around 45% to 75%. The higher the ethylene content the higher the loading possibilities of the polymer, better mixing and extrusion. Peroxide curing these polymers give a higher crosslink density compared with their amorphous counterpart. The amorphous polymer are also excellent in processing. This is very much influenced by their molecular structure. The dienes, typically comprising between 2.5 wt% up to 12 wt% of the composition serve as crosslinks when curing with sulphur and resin, with peroxide cures the diene (or third monomer) functions as a coagent, which provide resistance to unwanted tackiness, creep or flow during end use.
EPDM rubber is used in vibrators and seals; glass-run channel; radiator, garden and appliance hose; tubing; washers; belts; electrical insulation, and speaker cone surrounds. It is also used as a medium for water resistance in electrical cable-jointing, roofing membranes, geomembranes, rubber mechanical goods, plastic impact modification, thermoplastic, vulcanizates, and many other applications.
EPDM exhibits satisfactory compatibility with fireproof hydraulic fluids, ketones, hot and cold water, and alkalis, and unsatisfactory compatibility with most oils, gasoline, kerosene, aromatic and aliphatic hydrocarbons, halogenated solvents, and concentrated acids.
The main properties of EPDM are its outstanding heat, ozone and weather resistance. The resistance to polar substances and steam are also good. It has excellent electrical insulating properties.
Typical properties of EPDM vulcanisates are given below. EPDM can be compounded to meet specific properties to a limit depending first on the EPDM polymers available, then the processing and curing method(s) employed. EPDMs are available in a range of molecular weights (indicated in terms of Mooney viscosity ML(1+4)@125°C), varying levels of ethylene, third monomer and oil content.
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Mechanical Properties |
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Hardness, Shore A |
40 - 90 |
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Tensile Failure Stress, Ultimate |
25 MPa |
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Density |
Can be compounded from 0.90 to >2.00 gcm-³ |
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Thermal Properties |
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CTE, linear 68°F |
875µm m-1 °C-1 |
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Maximum Service Temperature, Air |
100-120 °C |
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Minimum Service Temperature, Air |
-54 °C |
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Glass Temperature |
-54 °C |
EPDM rubber is commonly used in weatherseals on all vehicles. This includes door seals, window seals, trunk seals, and sometimes hood seals. Frequently these seals are the source of noise due to movement of the door versus the car body. This is due to friction between the EPDM rubber and the mating surface (car painted sheet metal or glass). This can be alleviated using specialty coatings that are applied at the time of manufacture of the weatherseal, not as an aftermarket application. Such coatings can also greatly increase the chemical resistance of EPDM rubber. Some vehicle manufacturers such as General Motors also recommend a light application of silicone dielectric grease to weatherstripping to reduce noise.
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